1. Field of the Invention
The present invention generally relates to an inner-rotor motor and, more particularly, to an inner-rotor motor which does not form any electrical conducting path between an iron core and a housing of the motor.
2. Description of the Related Art
A cooling fan 9 having a conventional inner-rotor motor is shown in FIG. 1 and includes a stator 91, a rotor 92 and an impeller 93. The stator 91 and the rotor 92 jointly form the conventional inner-rotor motor. The stator 91 includes a housing 911 and an iron core 912 coupled to an inner surface of the housing 911. The rotor 92 includes a shaft 921 and a permanent magnet 922 coupled to an outer circumferential surface of the shaft 921. The rotor 92 is rotatably coupled inside the stator 91, and a gap is formed between the permanent magnet 922 and the iron core 912. One end of the shaft 921 extends outside the housing 911 for coupling with the impeller 93. As such, the stator 91 is able to drive the rotor 92 to rotate, and the impeller 93 is thus driven to rotate for cooling purposes.
In the conventional inner-rotor motor, the stator 91 is press fitted fit to the inner surface of the housing 911. Therefore, the iron core 912 is able to be adhered to the housing 911 closely. However, a conducting wire may be arranged outside the housing. In addition, the housing 911 is made of metal, and the iron core 912 is also made of a conductive material such as a silicon steel plate. Since the iron core 912 is adjacent to the housing 911, the conducting wire may easily cause electromagnetic interference to the iron core when electrified. Thus, noise and vibration are generated during rotation of the inner-rotor motor, and the operational stability of the inner-rotor motor is adversely affected.
Furthermore, in the case that the conducting material of a coil 913 arranged on the iron core 912 is exposed to air due to the wearing of the insulating coating, an electrical conducting path may be formed between the iron core 912 and the housing 911 since the iron core 912 is made of silicon steel plates and the housing 911 is made of metal. Thus, a leakage current may be generated on the exposed portion of the conducting material of the coil 913. In addition, the shaft 921 of the rotor 92 of the inner-rotor motor is usually coupled to the housing via a bearing 94. The bearing 94 is able to rotate relative to the housing 911 for rotatably coupling the rotor 92 inside the stator 91. When the bearing 94 is in the form of a conventional bearing structure such as a ball bearing or a sleeve bearing, the leakage current of the coil 913 may directly flow to the outer surface the inner-rotor motor via the iron core 912, the housing 911, the bearing 94 and the shaft 921. Thus, the safety of the inner-rotor motor is significantly reduced.
In light of the above, since the operational stability and safety of the conventional inner-rotor motor are poor, it is necessary to improve such an inner-rotor motor for increasing its market value.